The use of double metal cyanide catalysts in the preparation of high molecular weight polyols is well-established in the art. For example, U.S. Pat. No. 3,829,505, assigned to General Tire & Rubber Company, discloses the preparation of high molecular weight diols, triols etc., using these catalysts. The polyols prepared using these catalysts can be fabricated to have a higher molecular weight and a lower amount of end group unsaturation than can be prepared using commonly-used KOH catalysts. The '505 patent discloses that these high molecular weight polyol products are useful in the preparation of nonionic surface active agents, lubricants and coolants, textile sizes, packaging films, as well as in the preparation of solid or flexible polyurethanes by reaction with polyisocyanates.
Polyols prepared using double metal cyanide catalysts contain catalyst residues that interfere with the subsequent use of the polyol in a subsequent polyurethane-forming reaction. More specifically, the catalyst residues will cause undesirable side reactions to form unwanted by-products such as allophanates. Attempts have been made in the past to remove the catalyst residues from the polyol after production of the polyol. For example, U.S. Pat. No. 4,355,188 teaches that removal of the double metal cyanide catalyst residues can be effected by adding to the polyol-residue mixture a strong base selected from potassium hydroxide, potassium metal, and sodium metal in order to convert the residues to ionic species, and adding ethylene oxide while the base is in contact with the polyol. The ionic species are then separated by filtration, for example by contact with an ion exchange resin, in order to provide a purified polyol essentially free of the residues. Unfortunately, the use and handling of sodium or potassium metal poses an unwanted fire and explosion hazard.
As another illustration, U.S. Pat. No. 4,721,818 discloses a process which comprises (a) incorporating into the catalyst residue-containing polyol an effective amount of an alkali metal hydride in order to convert the double metal cyanide complex catalyst into an insoluble ionic metal species separable from the polyol, and wherein the polyol hydroxyl groups are also converted to alkoxide groups, and (b) separating the insoluble ionic metal species from the polyol. Practical application of this process requires an intermediate step between steps (a) and (b) involving the incorporation of an effective amount of ethylene oxide ("EO") into the catalyst residue-containing polyol/alkali metal hydroxide mixture in order to "EO cap" the polyol, and hence convert the secondary hydroxyl groups of the polyol to primary hydroxyl groups. Unfortunately, when following this procedure, a relatively low percentage of primary hydroxyl groups is obtained using a conventional amount of base, as described more fully in Part C of the working example provided hereinbelow. If the amount of base is increased, the primary hydroxyl groups can also be increased; however, the base separation problem becomes more difficult.
As yet another illustration, U.S. Pat. No. 4,877,906 discloses a complicated method involving (a) treating a DMC catalyst residue-containing polyol with alkali metal compound(s), (b) filtering and (c) treating the filtered polyol with a phosphorous compound to convert the soluble portion of the DMC catalyst residue into an insoluble portion, (d) filtering again, and then (e) recovering the polyol. This process is not as simple and straightforward as might be desired, and the phosphorous compound itself can cause a residue problem in the polyol.
The processes disclosed in the above discussed patents have the disadvantage of being applicable only to specific polyols and utilizing treatment chemicals which themselves cause the formation of residues in the polyol. New approaches, for providing catalyst residue removal and efficient EO capping with a high percentage of primary hydroxyl groups in the polyol, that are inexpensive, generally applicable to all polyols, and do not themselves cause a residue problem would be highly desired by the polyol manufacturing community.